Pulse recording apparatus



10, 5 J. P. ECKERT, JR, ETAL 2,536,100

PULSE RECORDING APPARATUS Original Filed May 27, 1948 6 Sheets-Sheet l IN V EN TOR.

JOHN PRESPER ECKERT, JR. JOHN CLARK SIMS, JR.

HER RT FRAZER WELSH 02 fil ATT RNEYS.

PULSE RECORDING APPARATUS 6 Sheets-Sheet 2 Original Filed May 27, 1948 IN VEN TOR.

JR. JR WELSH JOHN PRESP JOHN CLARK HE ERT FRAZ BY ZZZ ER ECKERT sms n ATT RNEYS.

Aug. 10, 1954 J. P. ECKERT, JR., EIAL 2,686,100

PULSE RECORDING APPARATUS Original Filed May 27, 1948 6 Sheets-Sheet 3 FIG.2.

IN V EN TOR.

JOHN PRESPER EGKERT, JR.

JOHN CLARK SIMS, JR.

ATTORN YS.

Aug. 10, 1954' J. P. ECKERT, JR.. ETAL 2,686,100

PULSE RECORDING APPARATUS Original Filed May 27, 1948 6 Sheets-Sheet 4 INVEN JOHN PRESPER ECKER R.

JOHN CLARK SIMS, JR.

HERB TFRAZER WELSH BY AZ K1 AT TO NE YS.

g- 1954 J. P. ECKERT, JR., ETAL 86,100

PULSE RECORDING APPARATUS 6 Sheets-Sheet 5 Original Filed May 27, 1948 INVENTOR. ECKERT sms, JR.

JOHN PRESPER JOHN CL-ARK HERB RT FRAZER WELSH BY ATTO NEYS Aug. 10, 1954 J. P. ECKERT, JR, ETAL 2,686,100

PULSE RECORDING APPARATUS Original Filed May 27, 1948 6 Sheets-Sheet 6 FIG. 8.

IN V EN TOR.

JOHN PRESPER ECKERT, JR. JOHN CLARK SIMS, JR..

HERB RT FRAZER WELSH BY fi/J ATTO NEYS Patented Aug. 10, 1954 UNITED STATES t me arsm OFFICE PULSE RECORDING APPARATUS signors, by mesne a Delaware Rand Inc., New Yoi Original application Ma 29,434. Divided and Philadelphia, Pa., as-

ssignrnents, to Remington k, I. 1 a corporation of y 27, 1948, Serial No.

this application April 12,

1949, Serial No. 87,056

21 Claims. 1

This invention relates to magnetic or similar recording apparatus and has particular reference to the recording of information on magnetic tape in coded form and the reproduction of such information from the tape through a relatively slowly acting mechanism such as an electrical typewriter. While certain aspects of the invention relate to the use of magnetic tape containing a plurality of recording channels, other aspects could equally relate to magnetic wire recording and reading. For simplicity of description tape will be referred to with the understanding that this term includes wire wherever the invention would be applicable thereto, 1. e., not necessarily directed. to multiple channel operations.

This application is a division of our application Serial Number 29,434, filed May 27, 1948, now Patent No. 2,625,607.

In devices for reading out information recorded magnetically on tapes, as in sound reproducing systems, it is customary to move the tape relatively to a pick-up unit at such a high rate of speed that the electrical output from the pick up unit is in the form of a sufliciently high frequency electric potential or current, and of sufficient magnitude above background noise, that amplification is readily effected to operate either a sound reproducer or other devices which are adapted to make use of the relatively high frequency output. Heretofore, magnetic tape re- 3-1 cording has been useful only when used in systems in which such a high frequency output can be utilized. Magnetic tapes, however, are well adapted for the storage of coded information in the way of minute magnetized spots thereon which, for convenience of terminology, will be hereinafter referred to as pulses; for example, as indicated hereafter a magnetic tape may very well be provided with multiple lengthwise channels carrying pulses selectively arranged so that a particular combination of pulses existing in corresponding positions in the various channels may represent numbers, letters, punctuation, machine instructions or other information. In most instances, however, the information thus carried by a tape cannot be utilized at the rate of delivery of the information through a pick-up head corresponding to such linear speeds of the tape as would give rise to output signals of a magnitude which could be amplified and utilized. As an example, suppose it is desired to use the tape to control an electric typewriter. In such a case the information which may determine the printing by a particular key of the typewriter may be represented by pulses having a length along the tape of no more than, say, ten thousandths of an inch, and for conservation of the tape the particular arrays of pulses representing different characters to be typed would not be spaced more than a few thousandths of an inch along the length of the tape. If the typewriter is to be operated from the output of the pick-up without the interposition of intermediate memory devices, it is obvious that the speed of the tape must be correlated with the typing speed of the typewriter which may mean, for example, that no more than sixteen characters should be delivered by the tape per second. This would represent a very slow movement of the tape as at a rate, at most, of only a fraction of an inch per second with the result that only extremely small signals would be obtained from the pickup, quite impractical to segregate from background noise at an amplifier output.

It is one object of the present invention to provide means for reading information from a magnetic tape when the tape is essentially stationary or moving very slowly so far as its average speed of advance is concerned. Briefly stated, this result is secured, in a preferred embodiment of the invention, by imparting to the tape in the vicinity of a pick-up a rapid vibration of quite small amplitude so as to get an output signal involving a modulated carrier having the frequency of the vibration, the modulation depending upon the pulses on the tape. In accordance with the invention, however, other modulation methods may be used though, generally speaking, they are inferior in involving the necessity for avoidance of disturbing effects produced by the earths magnetic field or other stray magnetic fields.

It will be evident that by thus producing a modulated carrier information may be read from the tape as slowly as may be desired from the standpoint of the frequency of succession of the units of information and hence the invention applicable for the direct drive, without intermediate memory devices, of such mechanisms as typewriters or other printing apparatus or of card or tape punches or the like.

One of the broad objects of the present invention is concerned with the attainment of slow reading out of information in the fashion indicated.

A further object of the invention relates to the provision of means for making use of the modulated carrier of the type described. As will be evident, when the information is carried by a tape on a plurality of channels, the response of an ultimate device, such as a typewriter, must be determined by what is picked up from some points bearing a predetermined relationship with each other in the several channels. If conservation of the tape is to be achieved with very close spacing of the units of information along the length of the tape it will be obvious that extreme and practically unattainable accuracy of mechanical parts would be required to insure that corresponding modulations of the various carrier channels should be so precisely in phase as to exercise their results practically simultaneously. Another object of the present invention is, therefore, to provide a system which will insure the proper utilization of the signals delivered from a group of pick-ups to avoid reading errors while nevertheless permitting the maximum amount of information to be carried per unit length of the tape.

As will be evident from the detailed description hereafter, the attainment of the last mentioned object solves not only the problem of securing proper pick-up of signals from a number of channels of a slowly moving tape but also that of securing from a number of channels of a rapidly moving tape a number of substantially simultaneous signals despite inaccuracy of alignment of signals in the individual channels with respective heads. Hence this last mentioned ob ject is not limited to the use of a slowly moving tape; furthermore it is not limited to a modulalation system.

A further object of the invention is to provide a pick-up unit which will insure as nearly as possible simultaneous delivery from a tape of signals which should theoretically be delivered simultaneously. This unit is also designed to provide precise location of information on a tape. Furthermore, a circuit arrangement is provided for placing information on the tape which in its preferred form incorporates various circuit elements involved in reading the information from the tape thus leading to simplicity in a system which, in its entirety, permits storing of information on the tape by manipulation of a typewriter and reproduction from the tape on the same or a similar typewriter or on a battery of similar typewriters. Particularly it is an object of the invention to provide recording and pick-up assemblies of such type as to make easy precise duplication of construction so that tape records made on one mechanism may be read on another with assurance of accurate reproduction of the original recorded information. It will be obvious that certain as pects of the invention are applicable to recording on, and reproduction from, films or tapes on which recording is eifected photographically or by printing or other process rather than magnetically.

It is a further object of the invention to provide means for recording and reading out information to or from a number of very closely arranged channels on a tape without cross-talk during either recording or reproduction.

Another object of the invention relates to an improved means for securing modulated signals frcm a tape by causing vibration of the tape locally.

As will be later evident, some of the objects above are not limited to the reading of or recording on magnetic tape: but are applicable to other types of reading and recording involving, for ex ample, photographic film, perforated tape or the like.

These and other objects of the invention particularly relating to details of construction and operation will become apparent from the following description read in conjunction with the accompanying drawings in which:

Figures 1A and 1B are complementary wiring diagrams illustrating the wiring of the apparatus but involving, as shown, only the apparatus for a single channel together with those parts which are common to a complete group of channels;

Figure 2 is a block diagram which, considered in conjunction with Figures 1A and 113, will make clear the fashion in which control is cifected in the use of multiple channels;

igure 3 is an inverted plan View, partially in section, of a magnetic head unit used for both recording and reproduction;

Figure 4. is an end elevation of the same;

Figure 5 is a side elevation of the same;

Figure 6 is a transverse section taken on the plane indicated at 5-6 in Figure 3;

Figure '7 is a fragmentary sectional view illustrating the construction of a single head;

Figure 8 is an elevation, partly diagrammatic in character, illustrating a magnetic tape feeding device, together with the means for vibrat ing a portion of the tape in the direction of its length; and

Figure 9 is a sectional view illustrating certain switching elements of a conventional electrical teletypewriter.

There will first be considered Figures 1A and 1B which illustrate the electrical details and in terconnections of four types of elements, A, B, C and D which are bounded by the rectangles correspondingly designated. A represents what might be called an amplifier and phase detector element. B is a power amplifier involving a flipfiop which serves the purpose of providing a memory and holds the pulse or no-pulse condition of the read-in signal from a tape during the time that other channels are setting up in preparation for the parallel reading out from all channels. C is a timing and control element. D is a signal generator. Only one unit C and one unit D are included in a complete system. Of the elements A and B, however, there is one of each corresponding to each tape channel which is connected to the key and type mechanism of an electrical typewriter. For consistency of description it will be assumed that there are six such channels though the magnetic tape may contain additional channels utilized to carry control information; in fact, in Figures 3 to 7, inclusive, provision for eight channels is illustrated. Reference will be later made to Figure 2 to show how the elements which occur in multiple are connected into the system; Figures 1A and 13, however, show in detail only one element A and only one element B which would correspond to the same tape channel.

The coil of the recording and reproducing head of a channel is indicated at 2. As will be pointed out hereafter the same head is used for both purposes and references to recording and reproducing will be used only to distinguish the functions of the head directly under consideration. One of the terminals 5 of the coil 2 is connected to a line 5 which constitutes a common line for the corresponding terminals of all of the head coils. During reproduction this line is connected to zero potential; during recording it is connected to a positive 220 volt source. The other terminal 3 of the coil is connected to a singlepole double-throw switch l which may selectively connect it to contacts 8 and it]. In the figures under discussion there are a number of doublethrow switches illustrated and for consistency all of these switches are illustrated in the positions which they occupy when reading of the tape is to be effected.

As illustrated, the coil 2 is COllll"""Cl mary of the input transformer iii, the of which is tuned by a condenser i l to the st o.- ard frequency of the systen i. e., that frequency at which the tape is oscillated. Signals from the tuned secondary are passed through condenser l 6 to the control grid of a pentode amplifier tube 13, there being provided a conventional grid resistor 20 and plate load resistor with ventional screen supply. Connected to the oathode is a fixed bias resistor :l by a condenser 30, this resistor potentiometer 32 which arrangement mentioned hereafter. The output from the plate of tube 38 passes through the condenser 34 to the control grid of a second pentode 36 having the conventional grid 38, a cathode biased resistor 46 bypassed by condenser 28 conventional s reen and plate connections, the plate resistor being shown 56, The output from this stage is delive ed through the condenser iii to the grid of the l ode 52 in a cathode follower circuit. Tie triode 52 has its grid resistor 3 connected to the junction of the cathode resistors and 8 acre which the signal is developed. The cathode 0 rent of this tube flows back through the line 85 and a portion of the potentiometer 32 so that there is developed a potential in the cathode circuit of the tube 28 providing inverse feedback to insure uniform gain characteristics of this amplifier system. Without such inverse feedback the amplifier would change its operating characteristics as the tubes and other components or the circuit age.

At this point it may be remarked that, to facilitate understanding of the operation by those skilled in the art, there are indicated at various terminals the direct potentials provided by a conventional power supply, the of which need not be considered since they well known; for example, it will be noted that the and screen potentials of the amplifying far described are provided from direct ositive 216 volt source while the lower end or" the pctentiometer 32 is connected to a zero voltage point in the system.

The amplified signal from three sta plifier which has been described is de -ve2 d. through the condenser 52 to the grid circuit of the triode 64. The signals developed the plifier are sufficiently large to drive the tube from below cut-off Well into saturation. The grid circuit of the tube includes two resistors 66 and The resistor es is such that when the output signal from the amplifier drives the grid of triode 64 positive the grid current flow through resistor to will provide a potential drop so as to prevent the grid from going substantially positive relative to its cathode. The of the wave is thus clipped. It will he noted. that the resistor 58 is returned to a potential of minus 70 volts, suinciently lower its cathode potential of minus 50 volts so that the triode 6% is completely out off when no signals are delivered to it. The purpose of the triode and its circuit is to transform approximately sinusoidal waves at the input of the amplifier 'o of approximately rectangular shape in the output from the triode. The use of the large negative bias on the grid of triode 36 inhibits operation of the trito the prisecondary is part of a ieed-back being in series with a ode until certain minimum signals have been delivered to it and thus it suppresses noise signals which may come through the amplifier but which are of less than a critical amplitude. The pulselike signals produced in the triode 6 5 across the resistor 70 Which connects the plate or" this triode with a positive volt potential. It may be noted that the arrangement described not only produces substantially rectangular pulses but pulses which are also relatively narrow as compared with the half period of a substantially sinusoidal input.

These narrow pulses are fed to a diode gating circuit providing phase detection. To the plate of triode (it are connected the anodes of diodes 2 and "M, which (as well as other diodes indicated hereafter) may be of the germanium crystal type, in series with respective resistors and '58 which have common return to the nega tive 70 volt potential source for the grid of triode G l. (It may be here noted that, throughout the drawings, the arrow heads in diodes indicate their cathodes while the orthogonal lines indicate their anodes.) When no signal or a negative signal is delivered to the triode its grid will be in cutoff condition and its plate, in the absence of the diodes and their connections, would rise to the plus 85 volt potential to which the plate resistor is is connected. However, since diodes are connected through their resistors to the negative potential source they will and the current flow through the resistor iii will decrease the maxim n1 potential to which 0 plate of triode may rise by reason or the dr through resistor ill. Although the return is a negative '70 volt potential, under these conditions of zero or negative signal to the grid of trio'de 64 the cathodes of the diodes 72 and i l will be at a positive potential with respect to the zero reference potential, the resistors 8, l6 18 having values to secure this con: on consistent with the total current flows therein.

If the circuit so far described up to ineluding the triode t-t is examined it will he noted that a positive swing of the control grid of the tube ill will produce a negative pulse at the anode f the tride 64. These negative pulses have their peaks below the zero of potential and if it were not for additional current flow to the caodes of the diodes l2 and 74 their cathodes would be rendered negative by reason of the connections through the resistors l5 and is to the negative potential source. However, as will be pointed out shortly, this does not occur until a coincideuce occurs between a negative pulse at the anode of the triode 54 with negative pulses provided from the signal generator which will now be described. To complete description of the element A, however, it may he noted the cathodes of the diodes ar l i spectively connected through crystal d and 83 to lines 86 and 34. Furt ermore, tl respectively connected through the rangement of diodes :3 and H38, and respectively, to the lines i 82 and t2. the cathode of the diode F2 is connec the crystal diode $5 to the line its. ioted that in all of connected together. The various lines just mentioned will reappear hereafter.

The signal generator indicated at D consists of an oscillator I lit which may be of any suitable type but which is illustrated as of the Colpitts type. This consists of a tried-e Hi8 having plate resistor Hi3 connected to a positive potential source. Signals appearing across this plate resistor are fed back to the grid circuit through an inductor H2 in series with a condenser H6, both being shunted by the condenser lid. From the junction point H8 connection is made through the condenser I20 to the grid of the triode Hi8, there being provided the usual grid resistor I22. This oscillator operates in conventional fashion to provide an output at the frequency at which it is desired to oscillate the tape from which signals are being read.

The output from the plate circuit of the oscillator is fed through blocking condenser iii i to the grid of the triode I26 which acts as a phase inverter. its connected to the junction of the two cathode resistors Hill and I32. These two cathode resistors have a total series resistance approximately equal to the resistance of plate resistor its and thus the signal developed across the resistor 53 is approximately equal to that developed across the series arrangement of the resistors I36 and 132. The signals, however, will be 180 out of phase with each other. These signals are fed through blocking condensers lit and E38 to the control grids of the triodes hill and Hi? which act as power amplifiers. The input resistors its and use of these tubes are'returned to zero potential while the cathodes of the tubes Hill and ii are returned to zero potential through a common bias resistor I48. The plates of the two tubes are and M2 are connected in push-pull to an output transformer I in the manner normally used for audio power drive. The secondary I52 of the transformer 1% is matched with and connected to the tape oscillating driver as will be described hereafter, the connection of this being to the terminals I53 and 455 of the transformer secondary. It will be noted that the terminal !55 is grounded.

The terminal I53 is connected through the line 55'! to a phase shifter comprising the variable resistor 156 and the condenser 55. The purpose of this phase shifter is to produce a shift in phase to compensate for any phase shift which may occur in the electromechanical device which oscillates the tape to insure coincidence of pulses as later described. Signals are fed from the phase shifter through blocking condenser its and resistor I62 to a conventional flip-flop IS- l of the Eocles-Jordan type which is well known in the art. Resistor IE2 is present to avoid interference by condensers W8 and N38 with the flipping action. High speed operation is not here required and hence the flip-flop can be of the type suitable for low speed operation. The output of the flip-flop delivered through the condensers Hi4 and IE6 will consist of square waves occurring at the frequency of the oscillator ice, but as delivered through the two condensers, 186 out of phase with each other. These condensers are connected to a pair of resistors I63 and Elli, the junction point of which connects with a negative '70 volt potential source. The signals through the condensers are transmitted to the grids of a pair of triodes I16 and H8 through resistors H2 and I'M. The plates of these triodes are connected to a positive 210 volt source through the resistors Hit] and I82. The condensers Hi l and IE6 in conjunction with the 1 resistors i68 and I perform differentiation upon the square wave signals, 1. e., their time constant is very short. Pulses will, therefore, be delivered to the grids of the triodes lie and 178 at the times the flip-flop I54 undergoes transi- This triode has a suitable grid resistor tion. Both tubes H6 and I18 are biased to cutoif and accordingly only positive pulses applied to their grids will be effective. Thus at the time of zero phase positive peaks, a positive pulse Will be delivered to the grid of the tube H3 through the condenser IE6. At the time of the peaks which are 180 out of phase a positive pulse will be delivered to the grid of the tube l'lii. These positive pulses applied to the grids produce negative pulses at the plates due to currents through the plate resistors I and lBZ. The potential to which the plates of the tubes llfi and H8 may rise at the times when their grids are cut-off is limited by the presence of the crystal diodes 883 and F86 which have a return to a positive 10 volt potential source. Negative pulses originating from a positive 10 volt origin are, therefore, delivered to the lines and 85.

-t is now possible to describe the gating action coniointly effected by the elements A and D which have so far been described. When no pulses are provided at the anodes of the crystal diodes l2 and 82 through their respective connections to the plate of triode 5d and to the line 86 these anodes will be positive and, consequently, current will flow through the resistor it to the negative 70 volt source and their cathodes will be at a positive potential. When a negative pulse emanating from the plate of triode es is imposed on the anode of the diode E2 in the absence of a simultaneous pulse through the line 85 the cathode of the diode l2 will be more positive than its anode and, consequently, the diode in eifect, open-circuited and its cathode takes the approximately 10 volt positive potential of the line 86. The same action occurs if a negative pulse through the line 86 is not coincident with a pulse from the triode 64, i. e., the junction of the cathodes of the diodes l2 and 82 remains positive. A positive condition at this junction involves a positive condition of the cathodes of the crystal diodes 96 and Q8 with respect to their anodes and accordingly no outputs will occur through the lines Hi l or Hi2.

However, coincidence of negative pulses delivered to the diodes l2 and 82 will remove both sources of positive potentials from their anodes and their cathodes will become negative through connection to the negative '70 volt potential source. Thus negative pulses will be transmitted through the diodes $36 and Hill and 58 to the lines Hill and 32. As will be hereafter described, these lines run to the grids of triodes having their cathodes at zero potential.

The above explanation identically applies to the diodes i i and 80 so that coincidence of negative pulses from the plate of triode 6d and. the line 84 will produce negative pulses through the crystal diodes 88 and St to the line $2, also connected to the grid of a triode having its cathode at zero potential.

In accordance with the phasing assumptions which have been made previously a positive sig nal applied to the grid of tube i8 occurring in zero phase, i. e., with the positive peaks at the terminal I53 will result in the production of a negative pulse through the line 92. On the other hand, if these two signals are out of phase there will occur at the time of a positive pulse at the grid of tube 18 negative pulses in the lines IE2 and I34. Summarizing, an in phase condition of the grid of tube [8 and terminal l53 will produce negative pulses in line 912; an out of phase condition of the grid of tube l8 and terminal I53 will produce 9 negative pulses in lines I02 and selective system is provided.

Referring now to the circuit element in Figure 1B, there is illustrated at 2% a flip-flop of Eccles-Jordan type comprising the triodes 282 and 2%. During the reading of signals from the tape, switches res and and 253? are in the positions illustrated. Switch 29: engages a contact to join the plate of triode 2% to the grid of triode 202 through resistance and switch 203. This grid is also joined to the line s2. The grid of triode 254 is connected through resistance 2% to the plate of :iode 2M and also through the switch 201 to the line it. Resistors 222 and its connect the grids to a negative potential. It will be noted that the cathodes of triodes 262 and 26d are returned to a zero potential. The plate of triode 24M is connected through a neon bulb tit and a series resistor ill! to a positive 125 volt potential. It is also connected through condenser iii? and resistor 220 to a negative 76 volt potential. The junction of the condenser 213 and resistor 226 is connected through resistor 222 to the grid of triode .224. The cathode of the triode am is connected to a negative 60 volt potential source. Its plate is connected to a positive 10 volt potential source through a resistor 226. Its plate is also connected to the line 223 which runs to the circuit ele: ent B hereafter described.

The anode of triode 2% is connected through the condenser 232, switch 233 and resistor 238 to the grid of triode 2535, the plate of which is connected to the line 2 16, extending to the circuit element B, and the cathode of which is at zero potential, a switch 235 in the position illustrated also connecting the line to zero potential.

When a pulse is first encountered on the magnetic tape by a head H its leading edge produces a signal which at the rid of the tube i3 is 180 out of phase with the output at the terminal i 53. Accordingly, negative pulses will be transmitted through the line 532 to the grid of the triode 2M cutting ofi this triode and extinguishing the neon bulb M5 by raising the plate potential of this triode to the positive 85 volt potential of its source so that the resulting potential drop of 40 volts across the neon bulb is insufficient to maintain current flow through it. At the same time the triode 2E2 is rendered conducting. At the time of this transition a positive pulse is emitted through the condenser 218. It may be here noted that the first negative pulse oelivered through the line i512 will throw the flip-flop 203 into the state just described and subsequent negative pulses through the line M2 will be without any action on the flip-flop. As will be evident hereafter, such an initial flipping pulse may originate in any one of a group of heads.

The condenser 218 in conjunction with the resistor 228 provides a difierentiating action so as to deliver a sharp positive pulse through the resistor 222 to the control grid of the triode 22s at the time the positive pulse is delivered through the condenser 2 it due to the transition of the hipfiop just described. The arrival of this sharp positive pulse at the of the tube causes a negative pulse to be developed at its plate which pulse will be emitted along the line 228, noting that the cathode of triode 22 is at a negative 60 volt potential while its anode connected to a positive volt potential. The circuit of the triode 224 is only sensitive to positive pulses delivered to it through the resistor 222, since it is normally cut-off by the negative potential of its grid with respect to its cathode.

H34. Thus a phase As the magnetic tape heads the trailing edge of a pulse will ultimately produce signals which at the grid of tube IE will be in phase with the output at the terminal i533. As indicated previously, a negative pulse will thus be produced through the line which will render the triode 262 of the flip-flop non-conducting and the triode conducting. The neon tube 2E5 will now be fired and a negative pulse will he transmitted through the condenser 2 it. This negative pulse, without effect on the circuit of tricde ll be transmitted to the grid of the tricde through condenser 32 and resistor 238, a sharp pulse due to differentiating action, to cause it to become momentarily non-conducting, interrupting the how of current to it through the re stor the crystal diode 25B and the line Ed t.

The circuit element B comprises a flip-flop 244, which constitutes a set-up device or register, including the tr 259 and in conventional connections. The line his is, during reading of tape, connected through the switch 2&2 to the grid of triode A neon lamp 2% in series with a resistor 2G? is illuminated when the tube 256 is conducting.

A negative pulse through the line its renders the triode non-conducting and the triode 258 conducting. The line 2h; is thus rendered more positive. Less current is accordingly drawn through the resistor 252 and the crystal diode 258 that the junction of the anodes of the diodes and is no longer prevented from going with respect to the cathode of a pentode which is connected to a positive 40 volt source. The control grid of this pentode is connected to junction just mentioned through a line 25 1 and resistor At the time the rlip-fiop 244 shifts as just described the grid of the pentode Elli} will remain at practically the same potential as it was previously, due to the current drawn through the diode 25% line 2M However, when a ne ative pulse is applied to th grid of the triode and this triode becomes non-conducting the potential at the grid of the pentodc 25c becomes positive with respect to its cathode and accordingly the pentode 2% becomes conducting, drawing a large current from the termi- Eli i through the switch 263 which is in the position illustrated. As will be described hereafter, this terminal is conn d through a solenoid of a corresponding crutch mechanism in the decoding machine or" an electric typewriter to positive sec volt potential.

foregoing description has mentioned only 'r'e circuit elements A and 13. Actually when a multiple channel tape is used there is one of each of these elements present for each channel while there is only one of each of elements 0 and D in the entire device. In order now to make clear the complete assembly, reference may be made to Figure which shows inter-conned tions for a multiple channel device. In Figure 2 there is indicated at B an electrical typewriter advances beneath the capable of encoding to produce magnetic pulses is to a major extent (except for merely diagrainined herein since its insession ternal devices are well known and are illustrated, for example, in the patents to Fitch et al. 2,161,564, dated June 6, 1939 and 2,165,247, dated July 11, 1939. The former patent illustrates the encoding device of the typewriter and from this it will be evident that depression of a particular typewriter key will efiect the transmission of pulses on six output channel lines, which pulses, as hereafter described, will provide the magnetic pulses in the various channels of the tape. The latter patent illustrates the mechanism by means of which pulses originating in six channels of a tape will, by the actuation of clutches and associated devices control the operation of the typewriter to print letters, numerals or characters which correspond to the pulse group on the tape. In the portion G or" the diagram there are illustrated a group of solenoids which are connected to a common positive 300 volt potential source and to lines 2% heretofore described. These solenoids are the clutch controlling solenoids illustrated in Patent 2,165,247.

In Figure 2 there are illustrated the first, second and sixth pairs of circuit elements A and B with the third, fourth and fifth omitted to simplify the diagram. It will, of course, be understood that these are present and are connected into the complete circuit in the same fashion as those illustrated. In Figure 2 there will be recognized the various lines interconnecting, and external to, the circuit elements described in detail. As will be noted, the lines 5, 92 and 102 from the circuit element C connect to all of the corresponding lines of the circuit elements A. The same is true of the lines t l and 86 from the circuit element D. Lines 228 and 240 from the circuit element connect with the corresponding lines of the circuit elements B. The corresponding circuit elements A and B of the same channel are connected by the lines we and 267. To the coils in the decoding portion G in the typewriter there extend the lines 26 from the elements B. From the encoding portion F of the typewriter there extend the separate channel lines [U5 to the elements '5 and also the lines 215 and 22! to the element C. (The last three lines have not yet been discussed.)

Before proceeding with the description of the overall tape reading operation and the operation of the typewriter thereby there will be described the mechanical and electromechanical elements involved in reading signals out of the tape and in imposing the magnetic pulses thereon. Referring first to Figures 3 to '7, inclusive, there is i1- illustrated therein the assembly of heads for the various tape channels. Blocks 3%, etc and 306, of non-magnetic material such as berylliumcopper, or hard bronze or brass which will resist abrasion when in contact with the magnetizable tape, are accurately machined and ground and assembled with shims 33 and 336 of non-magnetic material between them through the use of bolts 30% and 358 and aligning pins 330 and 332. The adjacent faces of these blocks are ground flat so as to insure close dimensional tolerances. Extensions 342 and 3M have bolted to their accurately ground side faces guiding discs tit and Sill for the tape. Milled slots 32% and 322 are provided in the adjacent faces of the blocks 3132 and 36 i, and 364 and 306, respectively. There are also milled out hollows 32 and 326 for the reception of the coils of the heads, the leads from which pass out through openings 325 and 32?. Within each of the slots 32B and 322 there are located the stacks of accurately dimensioned laminations 338 and 3 36 which form the mag netic cores of the heads. The laminations 340 carry the windings 352, see Figure '7 (which cor respond to the coils 2 of the wiring diagram), and interruptions in the continuity of the laminated cores are provided by the shims 33d and 336. These shims may be 0.0001 to 0.001 inch in thick ness and define the gaps in the individual heads which are required for both producing magnetization of the tape and for reading out the signals therefrom. To secure great accuracy, the grinding of the adjacent faces of the blocks may be accomplished with the laminated cores in place.

Between the various slots 320 and 322 there are sawed slots 328 into which there are driven, after assembly, thin sheets of soft iron which prevent cross-talk between adjacent heads. Through the presence of these soft iron shims cross-talk between the heads is reduced to less than 1%, though, without them, cross-talk to the extent of 30% would be expected in an arrangement involving eight channels on a tape of 8 millimeter width.

The entire assembly should be made with the greatest attention to dimensional accuracy since on it depends the accuracy of location of the magnetized spots on the tape and the proper reading of signals from these spots. The edge guides 316 and 318 should have only minute clearances with the edges of the tape so that it cannot move either laterally or in shew fashion with resultant uncertainty of its position relative to th heads. The relationships between the gaps in the heads and these guides must also be very accurately insured.

As will be noted from Figure 3 the heads are divided into two groups of four heads each in order to provide the necessary spacing for the reception of the coils consistent with the recording of the eight channels on a very narrow tape. The spacings between the respective gaps located by the shims 3351 and 33% of the two sets of heads must also be very accurately insured since, as will be obvious, the pulses which are simultaneously read are not distributed in a single line across the tape but rather along two lines having different spacing. When reference is made herein to aligned pulses or spots on the tape there will be understood that there is signified the group of pulses which are simultaneously produced or read in the operation of the device and which are aligned with the gaps of their respective channel heads even though they are not arranged in a single line across the tape. With Wider tapes or less channels, of course, all of the heads might have their gaps arranged side by side in a single transverse line.

Referring now to Figure 8, the head assembly which has just been described is indicated at H. The tape passes beneath this assembly which is rigidly held against vibration. A tape supply reel 35:] has its mounting shaft connected to a motor indicated at 352 which is continuously energized in a direction to take up the tape. A take-up reel 35 2 is similarly connected to a motor indicated at 355 which is also energized to take up the tape. The tape 3% extending from these reels passes over idler pulleys 36c and 366 about a drive wheel 358 faced with friction material, thence about idler pulleys 362 and 364, and about the curved lower ends of springs 316 and 318 supported at their upper ends on a fixed member 314. The lower ends of these spring members 316 and 318 are connected to a tape guide 38!] which,

in turn, is connected through a link 382 with the vibratory element of a driver 384 which ha a coil energized through the connections I53 and I 55 previously described. This driving device 386 may be in the form of a conventional loud speaker drive adapted to vibrate the members 376, 3'28 and 3% at a suitable signal frequency such as 200 to 500 cycles per second in the direction of the length of the portion of the tape passing beneath the head H.

A worm Sill driven by a motor 3'12 drives a wheel 368 connected to the wheel 358 to impart continuous motion to the tape or, if desired, interrupted motion depending upon the nature of the control of the motor 3Z2. For present purposes, it may be assumed that the motor :li2 runs continuously to feed the tape at a suitable linear speed across the head assembly. The motors 352 and 356 merely insure that the tape is properly taken up on the reels and exert only sufficient torque for that purpose.

From the construction described it will be evident that the small loop of tape below the idlers 352 and 354 is alone subject to vibration through the action of the driver 384 and that this vibration is in the direction lengthwise of the tape where it passes the pick-up heads. This vibration of the tape creates the signal which appears as an alternating current applied to the grid of the input pentode is.

Since the arrangement does not involve any motion or" the pick-up heads the device is substantially free of disturbances due to the magnetic field of the earth or other stray magnetic fields as contrasted with such devices as would involve vibration of the head or modulation of its magnetic circuit which would require a degree of shielding very difiicult to obtain in order t suppress to a satisfactory degree noise signals due to ambient magnetic fields. As also pointed out, the input circuit is of a type which removes the influence of any signals below a. certain level. As a result, reading out of the tape pulses can be effected in a thoroughly reliable fashion.

There may now be described the overall operation of the system in the matter of operation of the typewriter from the pulse groups in the chanhole of the tape.

As will be evident from the construction of the head assembly and from the fashion in which pulses are recorded on the tape the pulses which form a particular code group will be presented to the heads approximately simultaneously and, at any rate, in such fashion that the arrival of a peak of any pulse of a group will not precede the arrival of the leading slope of any other pulse of the group. By accurate construction of the head assembly as described this condition may be easily assured and, accordingly, it will be assumed as a condition preexisting for the operation of reading the tape now to be described.

Assuming phasing consistent with the preceding description (though, of course, an arbitrary 180 phase shift could be used by slight modification of the circuits) the arrival of the leading portion of the first pulse to reach its correspond ing channel head will give rise to an input signal at the tube it which will be 180 out of phase with the potential of the terminal l53. In accordance with the preceding description this will cause the emission of negative pulses along the lines I02 and HM. Preceding this, in the nipfiop 200 the triode 292 will have been non-com ducting and the triode 204 will have been conducting. The negative pulse which is now emitted through the line 02 will cause the triode 204 to become non-conducting and the triode 2G2 conducting. A positive pulse is thus provided to the grid of triode 225 and a negative pulse is applied from this tube along the line 228 to each flip-flop 244 in the circuit elements B corresponding to the various channels. It may be noted that this pulse is delivered through a diode 229. The purpose of this diode is to the flip-flop, upon being pulsed through the crystal, to become free: i. e. the diode permits the pulse to be delivered to the grid of triode 25s to initiate the flipping action; but once this has started i116 potential on this grid will not be restrained to assume the potential of the line 228 and it may become more negative than the potential of line 228. This results in faster flipping and more positive action. In each of these elements the triode 250 is thus rendered non-conducting and the triode 249 is rendered conducting. It is to be noted that since the line 102 is connected to all of the elements A the arrival of a pulse as just described in any of the channels will effect only one operation of the flip-flop 209 which, in turn, will eifect clearing of all of the flip-flops 244 to put them in condition stated, irrespective of their previous conditions. In the case of those flip-nope having non-conducting triodes 250 there will, of course, be no change effected. The conditions existing from a previous pulse group are thus cleared out of the device.

While only the first pulse emitted through the line lcZ efiects any action by throwing the flipflop 206 as stated, as the tape advances the leading portions of each of the tape pulses of the group, including the tape pulse which gave the first output through the line Hi2, will cause the emission of at least a plurality of negative pu..es through the lines I04. Following the clearing the presence of a pulse in any channel will, accordingly, through this line 104, render in the corr sponding nip-flop 244 the triode 24S non-conducting and the triode 250 conducting. The result is that the circuit element B corresponding to any channel involving a tape pulse will be set up so that the crystal gating arrangement, through the line 248, will be prepared for the reception of a pulse along the line 2 36 to eifect current flow through the tube 260.

Nothing will now occur until the peak of one of the tape pulses passes by the gap in its corresponding head which, as previously assumed, will occur only after all of the elements B will be set up corresponding to pulses of the group. Following this event there will be produced an in-phase signal at the grid of the tube 58. As previously described this will give rise to negative output pulse along the line s2 to the grid of the triode 2G2 causing thi tube to be-- come non-conducting and tube 254 to become conducting. A negative pulse is emitted through the condenser 232 producing a cut-off of tube 23 which, through the lines 249, will result in operation of the gating elements at the input to the tubes zoo in elements B. Accordingly, the tubes 260 which correspond to those channels containing tape pulses will provide current flow through the corresponding clutch controlling solenoids G of the decoding portion G of the electric typewriter. As described in ?atent 2,165,247 there is thus produced operation of the typewriter key bars to result in the typing of a letter, numeral or other character corresponding to the code group which has been read. It

will be noted that the operation of all of the solenoids is effected simultaneously and in accordance with the single signal which is produced by the most advanced peak of the tape pulses in a particular group. It will be evident that subsequent negative pulses delivered through the line 92 will have no efiect on the flip-flop 200 and the entire system is accordingly restored to the condition assumed existing at the beginning of this description of the tape reading operation.

It may be here noted that condenser 232 differentiates signals fed to it. This provides a time constant sufficiently short so that the brief pulse applied to the tube 234, while long enough to produce reliable actuation of the clutches by the typewriter receiving solenoids, will nevertheless be short enough to avoid double actuation which would involve printing a character twice. The proper time is provided by the combination of condenser 232 and resistor 236. The condenser 23 i, used in recording, has a much larger capacitance than condenser 232 since differentiation is not desired during recording, the timing being obtained from flip-flop 208 when connected as a delay flop.

At this point there may be indicated some typical data which has been found to give excellent results. A satisfactory frequency for the longitudinal vibration or oscillation of the tape has been found to be from 400 to 500 cycles per second. This frequency is sufficiently high so as not to impede or interfere with the operation of the typewriter and to give rise to signals of sufficient amplitude to be readily amplified and utilized in the system. On the other, the frequency in this range is not too high to give rise to resonant or other difficulties in the mechanical vibrating system. I

A satisfactory amplitude of vibration of the tape lies in the range of 0.001 to 0.002 inch.

The gaps in the heads may desirably be in the range from 0.0005 to 0.0015 inch. The spacing between pulses along a channel may be about 0.01 inch. The length of a pulse may be of the order of 0.005 inch or less. A linear movement of the tape to correspond to reading of eight pulse groups per second, i. e., a movement of about 0.08 inch per second, has been found very satisfactory with a typewriter tion at moderate speeds.

it is to be understood that the figures just given are those which have been used in a particular instance and are not to be regarded as critical or as restrictive of the invention. With higher speed typewriters, for example, it would be possible to read from the tape a substantially larger number of groups per second and with increased precision of construction of head assemblies and decrease of the head gaps the pulses on the tape may have reduced linear dimensions and may be more closely arranged. Even the conservative figures given, however, will show that a very large number of characters may be represented on a single foot length of tape.

A mathematical analysis of the reading of pulses from an oscillating tape in accordance with the described procedure shows that there are delivered from the head frequency modulated signals and leads to the following conclusions:

The signal output from the tape due to its oscillation increases substantially linearly with oscillation frequency.

The signal output from the tape increases with the amplitude of oscillation but not linearly and capable of opera- 16 reaches a maximum when the amplitude is close to a quarter cycle length of the pulse distribution along the tape.

If only frequencies close to the frequency of oscillation are ultimately passed then the wave shape of the original wave (if non-sinusoidal) is increasingly distorted with increasing amplitude of oscillation.

As will be evident from the foregoing, the circuits which have been described are applicable to a system in which modulation is eifected otherwise than by the oscillation of the tape, for example, by producing variations in the reluctance of magnetic circuits or the like.

It may also be noted that the system for securing the simultaneous delivery of pulse outputs from a plurality of channels despite possible slight misalignment of the pulses of a group is applicable to the use of a fast moving tape which, without being oscillated, will produce signals of sufficient magnitude to produce output pulses which are not submerged in a noise background. The delivery of a number of simultaneous output pulses may be triggered by the passage of the first peak of a group in essentially the fashion described.

It will also be evident that this matter of securing a simultaneous output from various channels despite small misalignments of pulses in the channels is applicable not only to magnetic tapes but also to other multiple channel recording as well, for example, such as may be provided photographically on film or by punched holes in tapes.

The arrangement by which reading is effected simultaneously from all of a plurality of channels triggered by the attainment of a predetermined condition in any one of them eliminates the necessity for having a sprocket arrangement for triggering the reading operation. Heretofore, for example, if pulses were to be read in groups from six channels, it was necessary to provide either actually or in effect a seventh channel to determine when reading from the six channels should be accomplished. In accordance with the present invention, the sprocketing channel is eliminated altogether. This is accomplished, when n channels are to be read, at no more expense than that of reducing the normally 2 possible pulse groups to 2-l pulse groups. In other words, the only restriction involved is that there cannot be read that pulse group represented by no pulse in any of the channels. The necessity for this may, of course, be very easily avoided. There is, accordingly, read every group which involves at least one pulse in any channel.

There may now be described the recording of pulses on the tape through the operation of the encoding device F of the typewriter. As will be evident, this result could be accomplished through the use of a circuit entirely independent of the circuit through which reading of the tape is effected, merely switching the heads from one circult to the other as might be required. However, conservation of parts in a complete recording and reading system makes it desirable to utilize as many elements as possible for the two purposes and, consequently, in the preferred system which is herein disclosed this is done, the transition from reading the tape to recording on the tape being accomplished by shifting all of the doublepole switches which are illustrated to their alternative positions. From this point in the description, therefore, it should be understood that such 1 7 a shift has been effected in the case of each switch.

With the exception of the head coils and the leads and 267 therefrom the circuit elements A and D are not used in the recording operation. There is now no necessity for oscillation of the tape and consequently the circuit element D may, if desired, be taken out of operation through any suitable switching means; however, no harm would be done by oscillating the tape during recording except for a slight lengthening of the re corded pulses. It will be assumed, however, that the tape is advanced at uniform speed past the heads without having oscillations imparted to it.

Assuming the double-throw switches to be in their positions alternative to those illustrated in Figures 1A and 1B and that none of the typewriter keys is depressed the condition of the system will be as follows:

Tube 259 will be cut off due to the low resistance path through the crystal 256, line 249 and triode 234 to zero potential which causes the grid of tube 260 to be negative with respect to its cathode. Under these conditions the grid of each tube 300 is at cathode potential so that the tube is highly conductive with the result that current flows from the positive 360 volt supply terminal through the tube 306, line 26?, switch 1, terminal 3, corresponding coil 2, terminal 4, common line 5 and switch 235 which now engages contact 23? connected to the positive 220 volt supply terminal. This condition exists in the elements A and B of each channel and accordingly each head has a current continuously flowing through it from its terminal 3 to its terminal 4.

Each head is accordingly energized to produce an erasing action on the tape to remove any pulses previously contained thereon and which, as will be pointed out below, are imposed on the tape in a condition of opposite magnetic polarity obtained by current flow in the opposite direction through the head coils.

The shifting of the switches 28!, 2&3 and 20? will have transformed the fli -ilop 2&9 into a flip-flop of delay type, i. e., the triode we of the flip-flop will be normally conducting and the triode 204 normally non-conducting. A negative pulse applied to the grid of the triode 202 will reverse this situation, but only for a limited time after which the flip-flop will return to its original condition. The positive 85 volt terminal from which the anodes of the tubes 202 and 294 are supplied is connected through the adjustable resistor 2I3, resistor 2H and resistor 2&9 to the anode of the crystal diode 22I which has a return through resistor 2H3 to a positive volt terminal. The anode of the crystal diode is connected to the grid of triode 2% through'the switch 203. As will be evident, this means that normally the grid of triode 202 is held positive. The anode of triode 204 is connected through switch 2M and condenser I99 to the junction of resistors 209 and 2H. Switch 201 disconnects the grid of triode 204 from line I02 but the grid remains connected to the anode of triode 282 through resistor 206 and also through resistor 208 to minus 60 volts.

As will be pointed out hereafter, negative pulses to throw the flip-flop 200 will be delivered through the line 2I5 and will be differentiated by the condenser 2| 1 and resistor 2I9 to produce sharp pulses through the crystal diode 22I to the grid of triode 202. When the flip-flop is thus thrown to its abnormal condition it will not return to its normal state until the lapse of a time period determined by the condenser I99 and the resistors 2H and 2I3. By adjustment of the latter this time period may be adjusted to fix the time of application of current for a pulse group thereby determining the lengths of the pulses recorded on the tape.

When the switches are shifted the attainment of th normal condition of the flip-flop 200, i. e., with the tube 2% non-conducting, will have resulted in the application of a positive pulse to the grid of triode 225 which, in the fashion previously described in connection with reading of pulses from the tape, will result in delivery of a negative pulse to the grid of triode 259 of flip-flop 244. This flip-flop accordingly will be in a condition in which the triode 249 is conducting and the triode 250 is not conducting. The result is a less positive condition of the line 248 and cathode of crystal diode 258. The tube 260 will accordingly be normally non-conducting as stated previously.

The conditions just described exist when no typewriter key is depressed, and action of erasing pulses from the moving tape occurs.

Reference to Patent 2,161,564 will make clear how depression of a typewriter key will close a selected group of switches to produce current flow through selected ones of six channel lines substantially simultaneously. In Figure 2 these switches are indicated at F connected to the lines I 05.

By the key action the lines I05 are thus connected to a bus which is connected to the line 22I. What occurs may be traced as follows: Starting from th negative 60 volt potential terminal which is permanently connected to the cathode of triode 224 the circuit may be traced through switch 225, the filter, comprising resistors 22? and 23I and condenser 223, line HI and bus bar F. Thence the circuit is completed through the switch contacts F which have been closed by the key operation and lines I to the various circuit elements B. In each of these the line I05 connects through resistor 03 and switch 242 to the grid of triode 2&9. A negative pulse from the negative 60 volt terminal is thus applied to shift th flip-flops 244 corresponding to the channels through which the negative pulses were delivered so that the flip-flops 2&4 are set up with a resulting more positive condition of the connection 248 of each to the cathode of the crystal diode 258 due to interruption of current flow through triode 249.

As illustrated in Figure 2 there is a seventh contact F connected to the line 2I5 which in the operation of the typewriter is connected to the bus F". The contact just mentioned is not illustrated in Patent 2,161,564 but will be described later with reference to Figure 9. The arrangement is such that movements beyond the closures of the individual line switches connect the line 2i 5 to the bus, 1. e., all of the selected contacts at F are completed before the contact at F'. As will be immediately described, the contact at F initiates the pulse eifecting recording and by the production of a single pulse insures that the recording starts at precisely the same instant in all of the channels. The action is more precise than dependence upon simultaneity of closure of the various channel switches. Actually these do close very nearly simultaneously and wher extreme precision is unnecessary to secure a maximum number of pulse groups per unit length of tape it will be obvious that the use of a single pulse to initiate recording may be 1-9 dispensed with, th recording beginning in such case at the time each individual channel switch is closed.

The connection of the line 2l5 to the bus results in application of a negative pulse to the differentiating circuit provided by the condenser 21!] and resistor 2I9 so that a sharp negative pulse is applied through crystal diode 22! to the grid of the triode 292 of flip-flop 2%. The resulting transition of the flip-flop produces a negative pulse through the condenser 23! to the grid of the triode 234. The resulting cutting ofi of this triode interrupts current flow through crystal diodes 255 with the result that the grid of each tube 260 corresponding to a channel in which recording is to be effected becomes positive and the tube becomes highly conducting. A circuit through each individual head which is to apply pulses to the tape may now be traced as follows: from the positive 220 volt terminal through contact 23l, switch 235, line 5, coil terminal 4, coil 2, terminal 3, switch I, line 261, resistor 36! and tube 260 to the plus 40 volt supply terminal. The heavy current thus flowing passing through the resistor 39! drives the grid of the tube 308 highly negative with respect to its cathode so that this tube is cut-off removing in effect the positive 300 volt terminal connected to its anode from the circuit. The current flow just mentioned, it will be noted, is in the direction from the terminal 4 to the terminal 3 oi each coil, opposite that previously flowing so that new recording will take place. The interval of recording, however, is terminated by the reverse flipping of the flip-flop 2% after the pre-set interval. When this occurs negative pulses delivered to the flip-flops 2% as above described will clear them to their normal conditions and result in interruption of the recording cur-rent flow, reestablishing the erasing current flow by cutting off tube 260 and again rendering tube 306 conducting. The entire system is thus restored to its initial condition ready for the next operation or" a typewriter key.

Figure 9 illustrates the fashion in which provision is made for closing the contact at F' to the line 2l5 previously described. Comparison with the disclosure of Patent 2,161,564 above mentioned will show that the rocking contacts 455 corresponding to those in the patent are provided below their pivots 51 with extensions 55 which are arranged to engage upwardly extending lugs on a slide Mil which is guided for horizontal movement by engagement of screws M2 and 474 within slots 6-13 and 415. A spring 41% urges the slide H toward the left. An insulated extension 180 at the right-hand end of the slide is arranged to close contacts 6'88 and 482 having the external connections 48d and see. As will beevident, whenever any one of the rocking contacts Q56 moves counterclockwise the switch 'contacts 418 and 482 will be closed. If, as usual, two banks of these switches are provided the two corresponding sets of contacts 418 and 382 will be-connected in series to provide for a definite single'closure of the series circuit. This circuit corresponds to the circuit between the contact involving F' and the bus F" in Figure 2.

It will be clear from the foregoing that the circuits which have been'described are not necess'arily limited to recording on or reading from magnetic tape as the record element. As a most obvious variant of the invention there may be cited recording on and reading from photographic film in "whichcase pick-up would involve photoelectric devices and recording would involve illumination of the film. It will be readily apparent to those skilled in the art how such substitutions may be made for the magnetic heads which have been described.

Furthermore, it will be evident that instead of a typewriter as the encoding and decoding device there may be used many other devices, including punched tapes or cards for inserting information into the system and printing or card or tape punch devices or the like for receiving the information from the system.

What we claim and desire to protect by Letters Patent is:

1. In combination, a plurality of magnetic recording heads, means for advancing a magnetic tape past said heads, said heads being related to said tape to record along parallel channels on said tape, set-up devices individual to said channels, means for delivering selectively to said setup devices signals to set said devices in active state, means individually conditioned by a corresponding one of said devices in its active state, means for delivering signals of predetermined duration through conditioned ones of said last named means to corresponding recording heads to effect recording of magnetic pulses in corresponding channels on the tape, and means for clearing all of said set-up devices from said active state.

2. In combination, a plurality of magnetic recording heads, means for advancing a magnetic tape past said heads, said heads being related to said tape to record along parallel channels on said tape, set-up devices of flip-flop type individual to said channels, means for delivering selectively to said set-up devices signals to set said devices in active state, means individuaily conditioned by a corresponding one of said devices in its active state, means for delivering signals of predetermined duration through conditioned ones of said last named means to corresponding recording heads to eiiect recording of magnetic pulses in corresponding channels on the tape, and means for clearing all of said set-up devices from said active state.

3. In combination, a plurality of magnetic recording heads, means for advancing a magnetic tape past said heads, said heads being related to said tape to record along parallel channels-on said tape, set-up devices individual to said channels, means for delivering selectively to set set-up devices signals to set said devices in active state, means individually conditioned by a corresponding one of said devices in its active state, means for delivering signals of predetermined duration through conditioned ones of said last named means to corresponding recording heads to effect recording'of magnetic pulses in corresponding channels on the tape.

a. In combination, a plurality of magnetic recording heads, means for advancing a magnetic tape past said heads, said heads being related to said tape to record along parallel-channels on'said tape, set-up devices of fiip-flop type individual to said channels, means for delivering selectively to said set-up devices signals to set said'devices in active state, means individually conditioned by a corresponding one of said devices in its active state, means for delivering signals of predetermined duration through conditioned ones of said last named means to corresponding recording heads to efiect recording of magnetic pulses in corresponding channels on the tape.

'5. In combination, 'a plurality of magnetic recording heads, means for advancing a magnetic tape past said heads, said heads being related to said tape to record along parallel channels on said tape, set-up devices individual to said channels, means for delivering selectively to said set-up devices signals to set said devices in active condition, mean for delivering auxiliary control signals, means jointly responsive to the devices in said active condition and to said auxiliary control signals to deliver pulses to said recording heads to efiect recording of magnetic pulses in corresponding channels on the tape, and means for clearing all of said set-up devices from said active condition.

6. In combination, a plurality of magnetic recording heads, means for advancing a magnetic tape past said heads, said heads being related to said tape to record along parallel channels on said tape, set-up devices individual to said channels, means for delivering selectively to said set-up devices signals to set said devices in active condition, means for delivering auxiliary control signals, and means jointly responsive to the devices in said active condition and to said auxiliary control signals to deliver pulses to said recording heads to efiect recording of magnetic pulses in corresponding channels on the tape.

7. In combination, a plurality of magnetic recording heads, means for advancing a magnetic tape past said heads, said heads being related to said tape to record along parallel channels on said tape, set-up devices individual to said channels, means for delivering selectively to said set-up devices signals to set said devices in active condition, means for delivering auxiliary control signals, means jointly responsive to the devices in said predetermined condition and to said auxiliary control signals to deliver pulses of active duration to said recording heads to effect recording of magnetic pulses in corresponding channels on the tape, means for clearing all of said setup devices from said active condition, and means energizing said heads to erase pulses from the tape except when said pulses are being recorded thereon.

8. In combination, a plurality of magnetic recording heads, means for advancing a magnetic tape past said heads, said heads being related to said tape to record along parallel channels on said tape, set-up devices individual to said channels, means for delivering selectively to said set-up devices signals to set said devices in active condition, means for delivering auxiliary control signals, means jointly responsive to the devices in said active condition and to said auxiliary control signals to deliver pulses to said recording heads to eifect recording of magnetic pulses in corresponding channels on the tape, means for clearing all of said set-up devices from said active condition, and means energizing said heads to erase pulses from the tape except when said pulses are being recorded thereon.

9. In combination, a plurality of magnetic recording heads, means for advancing a magnetic tape past said heads, said heads being related to said tape to record along parallel channels on said tape, set-up devices individual to said channels, means for delivering selectively to said setup devices signals to set said devices in active condition, means for delivering auxiliary control signals, means jointly responsive to the devices in said predetermined condition and to said auxiliary control signals to deliver pulses of active duration to said recording heads to efiect recording of magnetic pulses in corresponding channels on the tape, and means energizing said heads to erase pulses from the tape except when said pulses are being recorded thereon.

10. In combination, a plurality of magnetic recording heads, means for advancing a magnetic tape past said heads, said heads being related to said tape to record along parallel channels on said tape, set-up devices individual to said channels, means for delivering selectively to said setup devices signals to set said devices in active condition, means for delivering auxiliary control signals, means jointly responsive to the devices in said active condition and to said auxiliary control signals to deliver pulses to said recording heads to eifect recording of magnetic pulses in corresponding channels on the tape, and means energizing said heads to erase pulses from the tape except when said pulses are being recorded thereon.

11. In combination, a, plurality of recording devices, means for advancing a strip past said recording devices, said devices being related to said strip to record along parallel channels of said strip, set-up devices individual to said channels, means for delivering selectively to said setup devices signals to set the set-up devices in active condition, means for deliverin auxiliary control signals, means jointly responsive to the set-up devices in said active condition and to said auxiliary control signals to deliver pulses of predetermined duration to said recording devices to effect recording of pulses in corresponding channels on said strip, and means for clearing all of said set-up devices from said active condition.

12. In combination, a plurality of recording devices, means for advancing a strip past said recording devices, said devices being related to said strip to record along parallel channels of said strip, set-up devices of flip-flop type individual to said channels, means for delivering selectively to said set-up devices signals to set the set-up devices in active condition, means for delivering auxiliary control signals, means jointly responsive to the set-up devices in said predetermined condition and to said auxiliary control signals to deliver pulses of active duration to said recording devices to effect recording of pulses in corresponding channels of said strip, and means for clearing all of said set-up devices from said active condition.

13. In combination, a plurality of recording devices, means for advancing a strip past said recording devices, said devices being related to said strip to record along parallel channels of said strip, set-up devices individual to said channels, means for delivering selectively to said set-up devices signals to set the set-up devices in active condition, means for deliverin auxiliary control signals, and means jointly responsive to the set-up devices in said active condition and to said auxiliary control signals to deliver pulses of predetermined duration to said recording devices to efiect recording of pulses in corresponding channels of said strip.

14. In combination, a plurality of recording devices, means for advancin a strip past said recording devices, said devices being related to said strip to record along parallel channels of said strip, set-up devices of flip-flop type individual to said channels, means for delivering selectively to said set-up devices signals to set the set-up devices in active condition, means for delivering auxiliary control signals, and means jointly responsive to the set-up devices in said predetermined condition and to said auxiliary control sig- 23 nals to deliver pulses of active duration to said recording devices to effect recording of pulses in corresponding channels on said strip.

15. In combination, a plurality of recording devices, means for advancing a strip past said recording devices, said devices being related to said strip to record along parallel channels of said strip, set-up devices individual to said channels, means for delivering selectively to said set-up devices signals to set the set-up devices in active condition, means for delivering auxiliary control signals, means jointly responsive to the set-up devices in said active condition and to said auxiliary control signals to deliver pulses to said recording devices to eiiect recordin of pulses in corresponding channels on said strip, and means for clearing all of said set-up devices from said active condition.

16. In combination, a plurality of recording devices, means for advancing a strip past said recording devices, said devices being related to said strip to record along parallel channels of said strip, set-up devices individual to said channels, rneansfor delivering selectively to said set-up devices signals to set the set-up devices in active condition, means for delivering auxiliary control signals and means jointly responsive to the setup devices in said active condition and to said auxiliary control signals to deliver pulses to said recording devices to effect recording of pulses in corresponding channels of said strip.

17. In combination, a set of registers each having an active and an inactive state, a first signal source selectively activating said registers, a set of signal gates each conditioned by a corresponding one of each registers in its active state, a set of load devices each respectively connecting with one of said signal gates, and a second signal source delivering signals through said conditioned signal gates to said associated load devices.

18. In combination, a set of registers each having an active and an inactive state, a first signal source selectively activating said registers, a set of signal gates each conditioned by a corresponding one of said registers in its active state, a set of recording devices each respectively connecting with one of said signal gates, a second signal source delivering an impulse of predetermined duration through said conditioned signal gates to their respective recording devices, and means returning each of said registers to its inactive state.

19. In combination, a set of registers each hav-.

ing an active and inactive state, a set of signal gates each conditioned by a corresponding one of said registers in its active state, a set of recording devices each respectively connecting with one of said signal gates, a. signal responsive network delivering an impulse of predetermined duration fill through said conditioned signal gates to their respective recording devices, and a signal source selectively activating said registers, said signal source energizin said signal responsive network after activating said selected registers.

20. In combination, a set of registers each having an active and inactive state, a set of signal gates each conditioned by a corresponding one of said registers in its active state, a set of recording devices each respectively connectin with one 01" said signal gates, a signal responsive network delivering an impulse of predetermined duration through said conditioned signal gates to their respective recording devices, a signal source selectively activating said registers, said signal source energizing said signal responsive network after activating said selected registers, and means returning each of said registers to its inactive state a predetermined time after said signal responsive network is energized.

21. In combination, a set of flip-flop circuits each having setu and clearing input leads, and an output lead; a set of signal coincidence gates each having a first input lead respectively connecting with the output lead of one of said flipflop circuits, a second input lead, and an output lead; a set of recording devices each respectively connecting with the output lead of one of said signal gates; a signal responsive network having a first output lead connecting with the second input leads of said signal gates, a second output lead connecting with the clearing input leads of said flip-flop circuits, and an input lead: and a signal source having a first set of output leads for selectively energizing the setup leads of said flipflop circuits, anda second output lead for energizing the input lead of said signal responsive network after said first set of output leads have been selectively energized.

References Cited in the file of this patent UNITED STATES PATENTS- Number Name Date 2,378,383 Arndt, Jr June 19, 1945 2,918,388 Begun June 19, 1945 2,439,446 Begun Apr, 13, 1948 2,441,065 Green May 1, 1948 2,533,326 Putt Dec. 12, 1950 2,540,554 Cohen Feb. 6, 1951 2,549,071 Dusek Apr. 17, 1951 OTHER REFERENCES Publication: The Annals of the Computation Laboratory or Harvard University, vol. XVI,

1948; Title: Proceeding of a Symposium On Large scale Digital Calculating Machinery. Pages 267-378; Paper titled: Transfer Between External and Internal Memory, by C, Bradford Sheppard. 

